Optical reflection polarizer and projector comprising the same

ABSTRACT

The present invention provides a projector that stably displays high-contrast, bright images by improving light resistance and heat resistance of a polarizer. The projector includes: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. At least one of the two polarizers is a structural birefringent polarizing plate.

TECHNICAL FIELD

[0001] The present invention relates to a projector for displayingimages, and more specifically pertains to a polarizer that is disposedon a light-incoming side and/or a light-outgoing side of a liquidcrystal device.

BACKGROUND ART

[0002] Projectors have a liquid crystal light valve including a liquidcrystal device (a liquid crystal panel). Polarizers are generallydisposed on a light incoming surface and a light outgoing surface of theliquid crystal device. The polarizer functions to transmit apredetermined polarized light component, while removing the other lightcomponents.

[0003] A light absorbing-type polarizing plate is generally used for thepolarizer in the projector. A typical example of the lightabsorbing-type polarizing plate is obtained by uniaxially orienting afilm including iodine or dye molecules. The light absorbing-typepolarizing plate has a relatively high extinction rate and relativelysmall incident angle dependency but poor light resistance and heatresistance.

[0004] The recent demand for the enhanced brightness of projected imagesand the size reduction of the projector leads to higher output of thelight source device and size reduction of the liquid crystal device.This increases the luminous flux of light entering the polarizing plateand thereby raises the luminous flux density. Namely this raises theintensity of light entering the polarizing plate per unit area.

[0005] The raised intensity of light entering the polarizing plate perunit area undesirably increases thermal load applied to the polarizingplate. The light absorbing-type polarizing plate removes a non-requiredlight component by absorption and converts the absorbed light componentinto heat. The light absorbing-type polarizing plate has poor lightresistance and heat resistance and accordingly has difficulties inmaintaining the polarization characteristics over a long time period.The disadvantage of the prior art projector is thus incapability ofstably displaying high-contrast, bright images over a long time period.

DISCLOSURE OF THE INVENTION

[0006] The object of the present invention is thus to solve thedrawbacks of the prior art technique discussed above and provide aprojector that stably displays high-contrast, bright images by improvinglight resistance and heat resistance of a polarizer.

[0007] At least part of the above and the other related objects isattained by a projector as a first apparatus of the present invention.The projector includes: a light source device; an electro-optic devicethat modulates light emitted from the light source device; twopolarizers that are disposed respectively on a light incoming side and alight outgoing side of the electro-optic device; and a projectionoptical system that projects light output from the electro-optic device.At least one of the two polarizers is a structural birefringentpolarizing plate.

[0008] The structural birefringent polarizing plate may also be called ashape birefringent polarizing plate or a form birefringent polarizingplate.

[0009] This projector utilizes the structural birefringent polarizingplate, which hardly absorbs light and has relatively high lightresistance and heat resistance. The projector thus stably displayshigh-contrast, bright images, even when the light entering the polarizerhas a high intensity per unit area, due to an increase in light outputof the light source device or due to reduction of the size of theelectro-optic device.

[0010] When non-polarized light enters the polarizer disposed on thelight incoming side of the electro-optic device, the thermal loadapplied to the polarizer on the light incoming side becomes heavier thanthe thermal load applied to the polarizer on the light outgoing side. Insuch cases, it is preferable that the structural birefringent polarizingplate is provided at least on the light incoming side of theelectro-optic device.

[0011] When a predetermined polarized light enters the polarizerdisposed on the light incoming side of the electro-optic device, thethermal load applied to the polarizer on the light outgoing side becomesheavier than the thermal load applied to the polarizer on the lightincoming side. In such cases, it is preferable that the structuralbirefringent polarizing plate is provided at least on the light outgoingside of the electro-optic device.

[0012] In the above projector, the structural birefringent polarizingplate may be a wiregrid polarizing plate.

[0013] The wiregrid polarizing plate has a simple structure, whichfacilitates manufacture of the structural birefringent polarizing plate.

[0014] In accordance with one preferable application of the aboveprojector, the structural birefringent polarizing plate includes a lighttransmissive crystal substrate and a fine periodic structureperiodically formed in a predetermined direction on the lighttransmissive crystal substrate.

[0015] The light transmissive crystal substrate has a relatively highthermal conductivity and thus quickly releases heat generated byabsorption of light by the structural birefringent polarizing plate. Asapphire substrate or a rock crystal substrate are typical examples ofthe light transmissive crystal substrate.

[0016] In accordance with another preferable application of the aboveprojector, the structural birefringent polarizing plate is inclined to acenter axis of light illuminating the electro-optic device.

[0017] The inclined layout of the structural birefringent polarizingplate practically decreases the pitch of the fine periodic structurerelative to the incident light, thus improving the opticalcharacteristics of the structural birefringent polarizing plate.

[0018] In the above application, the structural birefringent polarizingplate may be arranged at an inclination of about 45 degrees relative tothe center axis.

[0019] When the light transmitted through the structural birefringentpolarizing plate is utilized for the electro-optic device, thisarrangement causes a non-required light reflected by the structuralbirefringent polarizing plate to be emitted in the direction of about 90degrees to the center axis. This arrangement prevents adverse effects ofthe non-required light on other optical elements. This arrangementfurther enables the light reflected by the structural birefringentpolarizing plate to be utilized for the electro-optic device.

[0020] In accordance with still another preferable application of theabove projector, the structural birefringent polarizing plate is dividedinto a plurality of areas, and at least one of the plurality of areas isinclined to a center axis of light illuminating the electro-opticdevice.

[0021] This arrangement relatively decreases the thickness of theinclined structural birefringent polarizing plate (that is, thedimension in the direction perpendicular to the light incoming surfaceof the electro-optic device). Part of the plurality of areas may bearranged perpendicular to the center axis of the light illuminating theelectro-optic device (that is, parallel to the light incoming surface ofthe electro-optic device).

[0022] In the above application, at least one of the plurality of areasin the structural birefringent polarizing plate may be arranged at aninclination of about 45 degrees relative to the center axis.

[0023] When the light transmitted through the structural birefringentpolarizing plate is utilized for the electro-optic device, thisarrangement causes the light reflected by the structural birefringentpolarizing plate to be emitted in the direction of about 90 degrees tothe center axis. This effectively prevents adverse effects of thereflected light on other optical elements. For the effective use of thelight reflected by the structural birefringent polarizing plate, thereflected light may be returned to the light source device forrecycling.

[0024] In accordance with one preferable embodiment of the aboveprojector, a light absorbing polarizing plate is further arranged on alight outgoing side of the structural birefringent polarizing plate.

[0025] The optical characteristics of the structural birefringentpolarizing plate have relatively large incident angle dependency andwavelength dependency. The optical characteristics of the lightabsorbing polarizing plate, on the other hand, have relatively smallincident angle dependency and wavelength dependency. The combined use ofthe light absorbing polarizing plate compensates for the incident angledependency and the wavelength dependency of the structural birefringentpolarizing plate, thus attaining the polarizer having excellent lightresistance, heat resistance, and optical characteristics. The structuralbirefringent polarizing plate and the light absorbing polarizing platemay be optically integrated with each other. The optical integrationreduces the loss of light occurring at their interface. A polarizingplate composed of an iodine or dye-containing material may be appliedfor the light absorbing polarizing plate.

[0026] In the projector of the above application, it is preferable thata light transmissive crystal substrate is further arranged on a lightoutgoing side of the light absorbing polarizing plate, and the lighttransmissive crystal substrate is appressed to the light absorbingpolarizing plate.

[0027] The arrangement of the light absorbing polarizing plate in closecontact with the light transmissive crystal substrate having arelatively large thermal conductivity facilitates release of the heatgenerated by absorption of light by the light absorbing polarizingplate. This arrangement thus relieves the deterioration of the opticalcharacteristics of the structural birefringent polarizing plate and thelight absorbing polarizing plate, due to the heat generated by the lightabsorbing polarizing plate.

[0028] In accordance with another preferable embodiment of the aboveprojector, a light reflective polarizing plate is further arranged on alight outgoing side of the structural birefringent polarizing plate.

[0029] The light reflective polarizing plate may be a multi-layeredpolarizing plate that is obtained by alternatively laminating abirefringent film and non-birefringent film.

[0030] The combined use of the light reflective polarizing plate,instead of the light absorbing polarizing plate, effectively compensatesfor the incident angle dependency and the wavelength dependency of thestructural birefringent polarizing plate, thus attaining the polarizerhaving excellent light resistance, heat resistance, and opticalcharacteristics.

[0031] The present invention is further directed as its second apparatusto a projector including: a light source device; an electro-optic devicethat modulates light emitted from the light source device; twopolarizers that are disposed respectively on a light incoming side and alight outgoing side of the electro-optic device; and a projectionoptical system that projects light output from the electro-optic device.At least one of the two polarizers includes: a first prism having alight incoming surface and a light outgoing surface, which face to eachother in a non-parallel orientation; and a light reflective polarizingplate that is disposed on a side of the light outgoing surface of thefirst prism. The light reflective polarizing plate divides light emittedfrom the first prism into first and second polarized lights havingdifferent polarizing directions, and transmits the first polarized lightwhile reflecting the second polarized light. An angle defined by thelight incoming surface and the light outgoing surface of the first prismis set to cause the second polarized light, which has been reflected bythe light reflective polarizing plate and returned to the first prism,to be totally reflected by the light incoming surface.

[0032] This projector utilizes the light reflective polarizer includingthe light reflective polarizing plate. This polarizer hardly absorbslight and has relatively high light resistance and heat resistance. Theprojector thus stably displays high-contrast, bright images, even whenthe light entering the polarizer has a high intensity per unit area, dueto an increase in light output of the light source device or due toreduction of the size of the electro-optic device.

[0033] This polarizer prevents the second polarized light reflected bythe light reflective polarizing plate from being emitted from the lightincoming surface of the prism to the outside. The light reflectivepolarizer disposed on the light outgoing side of the electro-opticdevice in the projector causes no light from the light reflectivepolarizer to enter the light outgoing surface of the electro-opticdevice, thus desirably preventing malfunction of the electro-opticdevice.

[0034] This polarizer has a prism. The relatively small setting for theangle defined by the light incoming surface and the light outgoingsurface of the prism reduces the size of the polarizer and thereby thetotal size of the projector.

[0035] In accordance with one preferable application of the aboveprojector, the first prism has an intersection line defined by the lightincoming surface and the light outgoing surface, and the intersectionline is substantially parallel to longer sides of a rectangular displayarea on the electro-optic device.

[0036] This arrangement further reduces the size of the polarizer andthereby the total size of the projector.

[0037] In accordance with another preferable application of the aboveprojector, a face of the first prism opposite to a vertical angledefined by the light incoming surface and the light outgoing surface ofthe first prism is set to cause the second polarized light totallyreflected by the light incoming surface to enter the opposite face atsubstantially right angles.

[0038] This arrangement causes the light entering the opposite face tobe mostly emitted from the opposite face, thus significantly decreasingthe light that is reflected by the opposite face and re-enters the lightreflective polarizing plate.

[0039] In the above projector, it is preferable that the first prism iscomposed of a material having a photoelastic constant of not higher thanabout 1 nm/cm/10⁵ Pa.

[0040] The prism composed of a material having a relatively lowphotoelastic constant causes substantially no change in polarizing stateof the light passing through the prism. The polarizer accordingly exertsthe excellent optical characteristics.

[0041] In one preferable application, the projector further includes asecond prism, which is disposed on a light outgoing side of the lightreflective polarizing plate to receive the first polarized lighttransmitted through the light reflective polarizing plate.

[0042] The traveling direction of the light emitted from the polarizeris regulated by adequately setting the refractive index of the secondprism and the angle defined by the light incoming surface and the lightoutgoing surface of the second prism. This enhances the degree offreedom in layout of other optical parts. Setting the shape and therefractive index of the second prism to be identical with those of thefirst prism gives the polarizer with substantially no change intraveling direction of the transmitted light.

[0043] In the above application, it is preferable that at least one ofthe first prism and the second prism is composed of a material having aphotoelastic constant of not higher than about 1 nm/cm/10⁵ Pa.

[0044] In the above application, it is also preferable that the secondprism is arranged to make a travelling direction of the first polarizedlight emitted via the second prism substantially coincide with atravelling direction of light entering the first prism.

[0045] This arrangement makes the traveling direction of the lightentering the polarizer substantially coincident with the travelingdirection of the light emitted from the polarizer, thus readilyconstructing the optical system including other optical parts. Thecoincidence of the traveling directions is attained by setting therefractive index of the second prism practically equal to the refractiveindex of the first prism, by arranging the light incoming surface of thesecond prism substantially parallel to the light outgoing surface of thefirst prism, and by arranging the light outgoing surface of the secondprism substantially parallel to the light incoming surface of the firstprism.

[0046] In accordance with one preferable embodiment of the aboveprojector, a light absorbing polarizing plate is disposed on a lightoutgoing side of the light reflective polarizing plate.

[0047] The light absorbing polarizing plate compensates for the incidentangle dependency and the wavelength dependency of the light reflectivepolarizing plate, thus giving the polarizer having excellent lightresistance, heat resistance, and optical characteristics. When thepolarizer includes the second prism, the light absorbing polarizingplate may be disposed either on the light incoming side or on the lightoutgoing side of the second prism.

[0048] In the above projector, the light reflective polarizing plate maybe a structural birefringent polarizing plate.

[0049] The structural birefringent polarizing plate is a lightreflective polarizing plate that hardly absorbs light and has relativelyhigh light resistance and heat resistance. The light reflectivepolarizer stably exerts the high optical characteristics even when thelight entering the polarizer has a high intensity per unit area. Atypical example of the structural birefringent polarizing plate is awiregrid polarizing plate.

[0050] In one preferable example of the above arrangement, thestructural birefringent polarizing plate has a fine periodic structureperiodically formed along a predetermined direction, and thepredetermined direction is substantially perpendicular to anintersection line defined by the light incoming surface and the lightoutgoing surface of the first prism.

[0051] This causes the structural birefringent polarizing plate to beinclined to the center axis of the light illuminating the electro-opticdevice. Such inclination practically decreases the pitch of the fineperiodic structure relative to the incident light, thus improving theoptical characteristics of the structural birefringent polarizing plate.

[0052] In the above projector, the light reflective polarizing plate maybe a multi-layered polarizing plate that is obtained by alternativelylaminating a birefringent film and non-birefringent film.

[0053] Application of the multi-layered polarizing plate for the lightreflective polarizing plate relatively reduces the incident angledependency and the wavelength dependency.

[0054] The present invention is also directed its third apparatus to aprojector including: a light source device; an electro-optic device thatmodulates light emitted from the light source device; two polarizersthat are disposed respectively on a light incoming side and a lightoutgoing side of the electro-optic device; and a projection opticalsystem that projects light output from the electro-optic device. Atleast one of the two polarizers includes a plurality of polarizerelements. Each polarizer element has: a first prism having a lightincoming surface and a light outgoing surface, which face to each otherin a non-parallel orientation; and a light reflective polarizing platethat is disposed on a side of the light outgoing surface of the firstprism. The plurality of polarizer elements are jointed in such a mannerthat the respective light incoming surfaces of the first prisms arelocated in a virtually same plane. In each polarizer element, the lightreflective polarizing plate divides light emitted from the first prisminto first and second polarized lights having different polarizingdirections, and transmits the first polarized light while reflecting thesecond polarized light. An angle defined by the light incoming surfaceand the light outgoing surface of the first prism is set to cause thesecond polarized light, which has been reflected by the light reflectivepolarizing plate and returned to the first prism, to be totallyreflected by the light incoming surface.

[0055] The polarizer included in the second apparatus discussed above isused for the polarizer elements, so that this projector exerts the samefunctions and advantages as those of the projector of the secondapparatus. Compared with the second apparatus using an integralpolarizer, this arrangement decreases the thickness of each polarizerelement and thereby reduces the total size of the polarizer. Applicationof the polarizer having the above construction to the projectoradvantageously reduces the whole size of the projector, compared withthe projector of the second apparatus.

[0056] The present invention is also directed as its fourth apparatus toa polarizer including: a first prism having a light incoming surface anda light outgoing surface, which face to each other in a non-parallelorientation; and a light reflective polarizing plate that is disposed ona side of the light outgoing surface of the first prism. The lightreflective polarizing plate divides light emitted from the first prisminto first and second polarized lights having different polarizingdirections, and transmits the first polarized light while reflecting thesecond polarized light. An angle defined by the light incoming surfaceand the light outgoing surface of the first prism is set to cause thesecond polarized light, which has been reflected by the light reflectivepolarizing plate and returned to the first prism, to be totallyreflected by the light incoming surface.

[0057] This polarizer is same with the polarizer used in the secondapparatus of the present invention and accordingly exerts the samefunctions and advantages.

[0058] The present invention is further directed as its fifth apparatusto a polarizer that includes a plurality of polarizer elements. Eachpolarizer element has: a first prism having a light incoming surface anda light outgoing surface, which face to each other in a non-parallelorientation; and a light reflective polarizing plate that is disposed ona side of the light outgoing surface of the first prism. The pluralityof polarizer elements are jointed in such a manner that the respectivelight incoming surfaces of the first prisms are located in a virtuallysame plane. In each polarizer element, the light reflective polarizingplate divides light emitted from the first prism into first and secondpolarized lights having different polarizing directions, and transmitsthe first polarized light while reflecting the second polarized light.An angle defined by the light incoming surface and the light outgoingsurface of the first prism is set to cause the second polarized light,which has been reflected by the light reflective polarizing plate andreturned to the first prism, to be totally reflected by the lightincoming surface.

[0059] This polarizer is same with the polarizer used in the thirdapparatus of the present invention and accordingly exerts the samefunctions and advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 is a plan view schematically illustrating the structure ofa main part of a projector PJ1 in a first embodiment;

[0061] FIGS. 2(A) and 2(B) illustrate some examples of the structuralbirefringent polarizing plate 200 shown in FIG. 1;

[0062]FIG. 3 is a sectional view schematically illustrating a structuralbirefringent polarizing plate 200A integrated a light absorbingpolarizing plate;

[0063]FIG. 4 is a sectional view schematically illustrating anotherstructural birefringent polarizing plate 200B integrated with a lightabsorbing polarizing plate;

[0064]FIG. 5 is a sectional view schematically illustrating stillanother structural birefringent polarizing plate 200E integrated with alight reflective polarizing plate;

[0065]FIG. 6 is a sectional view showing the structure of the lightreflective polarizing plate 250 of FIG. 5;

[0066] FIGS. 7(A) and 7(B) are plan views schematically illustrating thestructure of a main part of a projector PJ2 in a second embodiment;

[0067]FIG. 8 is a plan view schematically illustrating the structure ofa main part of a projector PJ3 in a third embodiment;

[0068] FIGS. 9(A) and 9(B) show modified examples of the structuralbirefringent polarizing plate of FIG. 8;

[0069]FIG. 10 is a plan view schematically illustrating the structure ofa main part of a projector PJ4 in a fourth embodiment;

[0070]FIG. 11 is a sectional view schematically illustrating thestructure of a first light reflective polarizer 1 in a fifth embodiment;

[0071]FIG. 12 shows setting for a vertical angle a of the prism 10;

[0072]FIG. 13 shows a modified example of the polarizer 1 of FIG. 11;

[0073]FIG. 14 is a sectional view schematically illustrating thestructure of a second light reflective polarizer 2 in the fifthembodiment;

[0074]FIG. 15 is a sectional view schematically illustrating thestructure of a third light reflective polarizer 3 in the fifthembodiment;

[0075]FIG. 16 is a sectional view schematically illustrating thestructure of a fourth light reflective polarizer 4 in the fifthembodiment;

[0076]FIG. 17 is a sectional view schematically illustrating thestructure of a fifth light reflective polarizer 5 in the fifthembodiment;

[0077]FIG. 18 is a plan view schematically illustrating the structure ofa main part of a projector PJ5 in the fifth embodiment; and

[0078]FIG. 19 shows layout of the light reflective polarizer 3′ disposedon the light outgoing side of the liquid crystal device 300 of FIG. 18.

BEST MODES OF CARRYING OUT THE INVENTION

[0079] Some modes of carrying out the present invention are discussedbelow with referring to drawings. In the drawings, X, Y, and Zdirections represent three different directions perpendicular to oneanother. In the description hereafter, light polarized in the Xdirection is referred to as X polarized light, while light polarized inthe Y direction is referred to as Y polarized light.

[0080] A. First Embodiment

[0081]FIG. 1 is a plan view schematically illustrating the structure ofa main part of a projector PJ1 in a first embodiment. The projector PJ1has a light source device 110, an integrator optical system 120, aparallelizing lens 190, a liquid crystal light valve LV, and aprojection optical system 500. The liquid crystal light valve LVincludes a liquid crystal device 300 that corresponds to theelectro-optic device of the present invention, and two polarizers 200and 400 that are disposed respectively on a light incoming side and alight outgoing side of the liquid crystal device 300. As discussedlater, in this embodiment, a structural birefringent polarizing plate,which is one type of light reflective polarizing plates, is applied forthe polarizer 200 on the light incoming side, whereas a light absorbingpolarizing plate is applied for the polarizer 400 on the light outgoingside.

[0082] The light reflective polarizing plate represents a polarizingplate that reflects a non-transmitted component of polarized light,whereas the light absorbing polarizing plate represents a polarizingplate that absorbs the non-transmitted component of polarized light.

[0083] The light source device 110 includes a light source lamp 111 anda reflector 112. Non-polarized light emitted radially from the lightsource lamp 111 is reflected by the reflector 112, so that substantiallyparallel light is emitted from the light source device 110 along anillumination optical axis L.

[0084] The integrator optical system 120 includes two lens arrays 130and 140. A plurality of small lenses 131 having a rectangular shape,which is substantially similar to the shape of a display area of theliquid crystal device 300, are arranged in a matrix on each of the lensarrays 130 and 140. The bundle of rays entering the first lens array 130is divided into a plurality of partial bundles by the respective smalllenses 131 and superimposed on the liquid crystal device 300 by thefunction of the second lens array 140. The integrator optical system 120thus equalizes an in-plane intensity distribution of the light emittedfrom the light source device 110 and illuminates the liquid crystaldevice 300 with the light. The light emitted from the integrator opticalsystem 120 enters the structural birefringent polarizing plate 200 viathe parallelizing lens 190.

[0085] The structural birefringent polarizing plate 200 converts thenon-polarized light emitted from the integrator optical system 120 to asubstantially one type of polarized light. The non-polarized light maybe regarded as a composite light of two different linearly polarizedlights having perpendicular polarizing directions. The structuralbirefringent polarizing plate 200 reflects one linearly polarized light,while transmitting the other linearly polarized light, so as to convertthe non-polarized light emitted from the light source device 110 tosubstantially one type of linearly polarized light. In this embodiment,the structural birefringent polarizing plate 200 transmits the Xpolarized light, which has been polarized in the X direction.

[0086] The liquid crystal device 300 is a transmissive-type liquidcrystal panel that modulates incident polarized light and emits themodulated polarized light. More specifically, the X polarized lightentering the liquid crystal device 300 is modulated, based on imageinformation given from external circuit (not shown), and the modulatedlight including a Y polarized light component is emitted from the liquidcrystal device 300.

[0087] The light absorbing polarizing plate 400 eliminates anon-required component from the modulated light emitted from the liquidcrystal device 300 to create light representing an image. Morespecifically, the light absorbing polarizing plate 400 is arranged tomake the direction of its transmission axis coincident with the Ydirection. The light absorbing polarizing plate 400 absorbs anon-required X polarized light component from the modulated lightemitted from the liquid crystal device 300 and transmits the Y polarizedlight component, thereby producing the image light. A uniaxial orientedpolarizing plate composed of iodine or dye molecules having a highextinction rate may be applied for the light absorbing polarizing plate400.

[0088] The projection optical system 500 projects the image lightproduced by the light absorbing polarizing plate 400 onto a projectionscreen 600. An image is accordingly displayed on the projection screen600.

[0089] FIGS. 2(A) and 2(B) illustrate some examples of the structuralbirefringent polarizing plate 200 shown in FIG. 1. The structuralbirefringent polarizing plate 200 is a polarizing plate having a fineperiodic structure periodically formed in a predetermined direction (inthe X direction). The element pitch in the fine periodic structure isset to be shorter than the wavelength of the incident light. Adequateselection of the material of the fine periodic structure and regulationof the pitch give a desired refractive index distribution and desiredoptical anisotropy, thus attaining desired polarization characteristics.

[0090]FIG. 2(A) is a perspective view schematically illustrating awiregrid-type structural birefringent polarizing plate 200. The wiregridpolarizing plate 200 has a structure made by depositing a metal thinfilm 211 on a light transmissive substrate 210 and forming fine grooves212 extending in the Y direction that separate the metal thin film 211.The metal fine periodic structure 211 reflects light in a wavelengthrange to be polarized. The metal thin film 211 may be composed ofaluminum or tungsten and is formed by vapor deposition or by sputtering.The fine grooves 212 may be formed by a combination of etching withtwo-beam interference exposure, electron beam lithography, or X-raylithography. The wiregrid-type structural birefringent polarizing plate200 has a simple structure and is thus readily manufactured.

[0091]FIG. 2(B) is a sectional view illustrating another example of thestructural birefringent polarizing plate 200. This structuralbirefringent polarizing plate 200 has a structure made by depositing amulti-layered film 215 on a light transmissive substrate 210 and formingfine grooves 212 extending in the Y direction that separate themulti-layered film 215. The multi-layered film 215 is obtained byalternately laminating two different dielectric thin films 213 and 214,which are isotropic but have different refractive indexes. Themulti-layered film 215 and the grooves 212 are formed in the same manneras the metal thin film 211 and the grooves 212 of FIG. 2(A).

[0092] Non-polarized light entering the structural birefringentpolarizing plate 200 having the structure as shown in FIG. 2(A) or FIG.2(B) is divided into a Y polarized light component, whose direction ofpolarization Y is the same as the direction in which the fine grooves212 extend, and an X polarized light component, which is perpendicularto the Y direction. The X polarized light is transmitted through thestructural birefringent polarizing plate 200, whereas the Y polarizedlight is reflected by the structural birefringent polarizing plate 200.Namely the structural birefringent polarizing plate 200 functions as thelight reflective polarizing plate that reflects the non-transmittedpolarized light. The structural birefringent polarizing plate 200 hasvery little light absorption in principle.

[0093] In actual use of the structural birefringent polarizing plate200, however, the fine periodic structure 211 slightly absorbs light andgenerates heat. In order to relieve the temperature rise in thestructural birefringent polarizing plate 200, a light transmissivecrystal substrate having a high thermal conductivity is desirably usedfor the light transmissive substrate 210. Such application ensures rapidand homogeneous dissipation of heat generated by the fine periodicstructure 211, and thereby gives the thermally stable structuralbirefringent polarizing plate 200.

[0094] The preferable material for the light transmissive crystalsubstrate has relatively high thermal conductivity and lighttransmittance. For example, a sapphire substrate mainly composed ofalumina (aluminum oxide) or a rock crystal substrate may be applied forthe light transmissive crystal substrate. The sapphire substrate has thethermal conductivity of about 50 times the thermal conductivity of astandard glass substrate and about 35 times the thermal conductivity ofa quartz glass substrate.

[0095] The structural birefringent polarizing plate 200 may also beobtained by orienting fine particles or fine crystals with shapeanisotropy or by forming a thin film (for example, an alumina) withpores according to the anodic oxidation method.

[0096] In principle, the polarization separation characteristics of thestructural birefringent polarizing plate have incident angle dependencyand wavelength dependency. These dependencies are reduced by making thepitch of the fine periodic structure sufficiently small relative to thewavelength of incident light. However, there is a manufactural limit tomake the periodic structure finer. Especially for the light in a shorterwavelength domain, the dependencies may thus not be reducedsufficiently. The combined use of another polarizing plate preferablycompensates for the polarization separation characteristics of thestructural birefringent polarizing plate as discussed below.

[0097]FIG. 3 is a sectional view schematically illustrating a structuralbirefringent polarizing plate 200A integrated a light absorbingpolarizing plate. This structural birefringent polarizing plate 200A hastwo different polarizing plates, that is, the structural birefringentpolarizing plate 200 shown in FIG. 2(A) and a light absorbing polarizingplate 220 disposed on the light outgoing side of the structuralbirefringent polarizing plate 200. The light absorbing polarizing plate220 is supported on a light transmissive substrate 210, which isarranged on the light outgoing surface of the structural birefringentpolarizing plate 200, to be in close contact with the light transmissivesubstrate 210. The light absorbing polarizing plate 220 is arranged tomake the direction of its transmission axis coincident with thedirection of the transmission axis of the structural birefringentpolarizing plate 200 (that is, the X direction). A uniaxial orientedpolarizing plate composed of iodine or dye molecules may be applied forthe light absorbing polarizing plate 220. Such light absorbingpolarizing plates are mass produced and inexpensive.

[0098] In the structural birefringent polarizing plate 200A, the twopolarizing plates, that is, the structural birefringent polarizing plate200 and the light absorbing polarizing plate 220, are opticallyintegrated with each other. The structural birefringent polarizing plate200 that hardly absorbs light and has excellent light resistance andheat resistance is disposed on the light incoming side, whereas thelight absorbing polarizing plate 220 that has excellent polarizationcharacteristics and relatively small incident angle dependency andwavelength dependency is disposed on the light outgoing side. Thecombined use of the light absorbing polarizing plate desirablycompensates for the incident angle dependency and the wavelengthdependency of the polarization separation characteristics in thestructural birefringent polarizing plate.

[0099] The above layout of the two polarizing plates relativelydecreases heat generation by the light absorbing polarizing plate 220,while improving the polarization characteristics of the structuralbirefringent polarizing plate 200A.

[0100]FIG. 4 is a sectional view schematically illustrating anotherstructural birefringent polarizing plate 200B integrated with a lightabsorbing polarizing plate. The structural birefringent polarizing plate200B includes a light transmissive crystal substrate 230, which isdisposed on the light outgoing side of the structural birefringentpolarizing plate 200A of FIG. 3.

[0101] In the structural birefringent polarizing plate 200A, the lightabsorbing polarizing plate 220 slightly absorbs light. This may causeheat distortion inside the light absorbing polarizing plate 220, whichleads to local variation in polarization characteristics. Arrangement ofthe light transmissive crystal substrate 230 having a relatively highthermal conductivity to be in close contact with the light absorbingpolarizing plate 220 as shown in FIG. 4 relieves the temperature rise inthe light absorbing polarizing plate 220. The structural birefringentpolarizing plate 200B accordingly has excellent polarizationcharacteristics.

[0102] The preferable material for the light transmissive crystalsubstrate 230 has relatively high thermal conductivity and lighttransmittance. For example, a sapphire substrate mainly composed ofalumina or a rock crystal substrate may be applied for the lighttransmissive crystal substrate 230. The light absorbing polarizing plate220 and the light transmissive crystal substrate 230 may be fixed andadhere to each other, for example, via an adhesive.

[0103] In the structure of FIG. 4, the light absorbing polarizing plate220 is interposed between the light transmissive substrate 210 and thelight transmissive crystal substrate 230. This structure homogeneouslyand evenly dissipates the heat generated by the light absorbingpolarizing plate 220. Thus, this structure effectively relieving thetemperature rise of the structural birefringent polarizing plate, due tothe heat generation in the light absorbing polarizing plate 220.

[0104] The structural birefringent polarizing plates 200A and 200B shownin FIGS. 3 and 4 relieve the incident angle dependency and thewavelength dependency of the structural birefringent polarizing plate200 and attain the excellent polarization characteristics. Thesepolarizing plates 200A and 200B are especially effective forilluminating systems using light of large divergence and illuminatingsystems using light in a short wavelength domain.

[0105]FIG. 5 is a sectional view schematically illustrating stillanother structural birefringent polarizing plate 200E integrated with alight reflective polarizing plate. The structural birefringentpolarizing plate 200E has a similar structure to that of the structuralbirefringent polarizing plate 200A shown in FIG. 3, except that thelight absorbing polarizing plate 220 is replaced by a light reflectivepolarizing plate 250. The light reflective polarizing plate 250 isdisposed to be in close contact with the light transmissive substrate210, which supports the structural birefringent polarizing plate 200E,and is optically integrated. The light reflective polarizing plate 250is arranged to make the direction of its transmission axis coincidentwith the direction of the transmission axis of the structuralbirefringent polarizing plate 200 (that is, the X direction).

[0106]FIG. 6 is a sectional view showing the structure of the lightreflective polarizing plate 250 of FIG. 5. The light reflectivepolarizing plate 250 is a multi-layered polarizing plate obtained byalternately laminating a first film 251 with birefringence and a secondfilm 252 without birefringence. The materials of the first film 251 andthe second film 252 are selected in advance to satisfy relations ofn1X≈n2 and n1Y≈n2, where n1X and n1Y denote refractive indexes of thefirst film 251 in the X direction and in the Y direction, and n2 denotesa refractive index of the isotropic second film 252.

[0107] The refractive indexes in the X direction at an interface betweenthe first film 251 and the second film 252 are practically equal to eachother, so that the polarized light in the X direction is transmittedwithout interference reflection. However, the refractive indexes in theY direction at the interface are different from each other, so that partof the polarized light in the Y direction is subjected to interferencereflection. The wavelength of the reflected light depends upon therefractive indexes and the thicknesses of the two films 251 and 252. Thereflectance depends upon the number of layers in the laminate and thebirefringence of the first film 251.

[0108] The adequate settings for the thicknesses and the refractiveindexes (materials) of the films 251 and 252 and the number of layers inthe laminate give the light reflective polarizing plate 250, whichtransmits substantially all the incident X polarized light whilereflecting substantially all the incident Y polarized light. Such alight reflective polarizing plate is described in detail, for example,in JAPANESE PATENT LAID-OPEN GAZETTE No. 9-506985 based on InternationalApplication.

[0109] Instead of the multi-layered polarizing plate discussed above, anoptical element including a cholesteric liquid crystal in combinationwith a λ/4 retardation plate, an optical element utilizing the Brewsterangle for separation into a reflecting polarized light and atransmitting polarized light (for example, SID'92 DIGEST p427), or ahologram optical element taking advantage of hologram may be applied forthe light reflective polarizing plate 250.

[0110] In the structural birefringent polarizing plate 200E (FIG. 5),the light reflective polarizing plate 250 is disposed on the lightoutgoing side of the structural birefringent polarizing plate 200. Thisarrangement prevents heat generation due to the light absorption. Thelight reflective polarizing plate 250 replacing the light absorbingpolarizing plate 220 of FIG. 3 also effectively compensates for theincident angle dependency and the wavelength dependency of thepolarization separation characteristics in the structural birefringentpolarizing plate.

[0111] Any of the structural birefringent polarizing plates 200A, 200B,and 200E may be disposed on the light incoming side of the liquidcrystal device 300, in place of the structural birefringent polarizingplate 200 shown in FIG. 1.

[0112] In the structural birefringent polarizing plates 200A, 200B, and200E, the structural birefringent polarizing plate 200 is opticallyintegrated with either the light absorbing polarizing plate 220 or thelight reflective polarizing plate 250. The two polarizing plates mayalternatively be separated from each other. The integration, however,reduces the loss of light occurring at the interface between the twopolarizing plates, thus enhancing the utilization efficiency of light.

[0113] As described above, in the projector PJ1, the structuralbirefringent polarizing plate 200 (200A, 200B, 200E) that hardly absorbslight is disposed on the light incoming side of the liquid crystaldevice 300. Such arrangement desirably reduces the heat generation inthe polarizer and thus maintains the characteristics of the polarizerover a long time period, even when the light entering the polarizer hasa high intensity per unit area, due to application of a light sourcedevice having a greater light output or due to application of a liquidcrystal device having a smaller display area. This actualizes aprojector that stably displays high-contrast, bright images.

[0114] The little heat generation in the polarizer may reduce the sizeof a cooling device, which is generally used in the conventional system,or even omit the cooling device, thus advantageously reducing the noiseand the whose size of the projector.

[0115] In the projector PJ1 of FIG. 1, the structural birefringentpolarizing plate 200 is disposed on the light incoming side of theliquid crystal device 300. This is because the non-polarized light isused as illumination light in the projector PJ1 and thereby a greaterthermal load is applied to the polarizer 200 disposed on the lightincoming side of the liquid crystal device 300, compared with thepolarizer 400 disposed on the light outgoing side. In the projectorutilizing non-polarized light as illumination light, it is effective toarrange a structural birefringent polarizing plate having high lightresistance and heat resistance on the light incoming side of the liquidcrystal device. The structural birefringent polarizing plate 200 mayalso be disposed on the light outgoing side of the liquid crystal device300.

[0116] B. Second Embodiment

[0117] FIGS. 7(A) and 7(B) are plan views schematically illustrating thestructure of a main part of a projector PJ2 in a second embodiment. FIG.7(A) shows the projector PJ2 seen from the Y direction, and FIG. 7(B)shows the projector PJ2 seen from the X direction. The same constituentsas those of the projector PJ1 of the first embodiment are expressed bythe same numerals and are not specifically described here.

[0118] The structure of the projector PJ2 in the second embodiment issimilar to that of the projector PJ1 in the first embodiment, exceptthat the integrator optical system 120 of FIG. 1 emitting non-polarizedlight is replaced by an integrator optical system 150 (hereinafter mayalso be referred to as ‘polarization conversion optical system’) thatconverts non-polarized light to substantially one type of polarizedlight and emits the polarized light. The integrator optical system 150of this embodiment emits X polarized light.

[0119] The position of the polarizers in the liquid crystal light valveLV is changed with the replacement of the integrator optical system.More specifically, in the projector PJ2 of this embodiment, thestructural birefringent polarizing plate 200 is disposed on the lightoutgoing side of the liquid crystal device 300, whereas the lightabsorbing polarizing plate 400 is disposed on the light incoming side.With the change in position of the polarizers, the light absorbingpolarizing plate 400 is arranged to make its transmission axiscoincident with the X direction. The structural birefringent polarizingplate 200 is arranged to make its periodic fine structure extend alongthe Y direction. The light absorbing polarizing plate 400 of thisembodiment accordingly transmits the X polarized light, while thestructural birefringent polarizing plate 200 transmits the Y polarizedlight.

[0120] The polarization conversion optical system 150 includes the firstlens array 130, the second lens array 140, a polarization beam splitterarray (hereinafter referred to as PBS array) 160, a selectiveretardation plate 170, and a superimposing lens 180. The PBS array 160includes a plurality of glass members having the cross section of aquasi parallelogram. Polarization separation films and reflection filmsare alternately formed on the interfaces of the adjoining glass members.

[0121] The bundle of rays entering the first lens array 130 is dividedinto a plurality of partial bundles by the respective small lenses 131.Each partial bundle is divided by the PBS array 160 into two linearlypolarized lights having perpendicular polarizing directions. Theselective retardation plate 170 functions to align the polarizingdirections of two linearly polarized lights. The polarized light (Xpolarized light) aligned to have substantially the same polarizingdirection is emitted via the superimposing lens 180 and are superimposedon the liquid crystal device 300 via the parallelizing lens 190 in thesame manner as the first embodiment.

[0122] Application of the polarization conversion optical system 150equalizes the in-plane intensity distribution of illumination lightentering the liquid crystal device 300, while ensuring emission of theillumination light having the substantially adjusted polarizingdirection with little loss of light. Such a polarization conversionoptical system 150 is described in detail in JAPANESE PATENT LAID-OPENGAZETTE No. 8-304739.

[0123] In the projector PJ2 of this embodiment including thepolarization conversion optical system 150, the polarizer 400 disposedon the light incoming side of the liquid crystal device 300 is utilizedto enhance the degree of polarization of the incident light. Theenhanced utilization efficiency of light by the polarization conversionoptical system 150 raises the intensity of the light entering thepolarizer 200 disposed on the light outgoing side of the liquid crystaldevice 300. Namely, the thermal load applied to the polarizer 400disposed on the light incoming side of the liquid crystal device 300 issmaller than that in the first embodiment, while the thermal loadapplied to the polarizer 200 disposed on the light outgoing side isgreater than that in the first embodiment. Because of this fact, in theprojector PJ2 of this embodiment, the light absorbing polarizing plate400 is disposed on the light incoming side of the liquid crystal device300, and the structural birefringent polarizing plate 200 is disposed onthe light outgoing side.

[0124] As described above, in the projector PJ2, the structuralbirefringent polarizing plate 200 that hardly absorbs light and hasexcellent light resistance and heat resistance is disposed on the lightoutgoing side of the liquid crystal device 300. Such arrangementdesirably reduces the heat generation in the polarizer and thusmaintains the characteristics of the polarizer over a long time period,even when the light entering the polarizer has a high intensity per unitarea, due to application of the polarization conversion optical system150. This actualizes a projector that stably displays high-contrast,bright images.

[0125] The structural birefringent polarizing plate 200 may be replacedby any of the structural birefringent polarizing plates 200A, 200B, and200E shown in FIGS. 3 to 5. Such replacement further enhances thecontrast of the displayed image. Any of the structural birefringentpolarizing plates 200, 200A, 200B, and 200E may also be applied for thepolarizer 400 disposed on the light incoming side of the liquid crystaldevice 300.

[0126] C. Third Embodiment

[0127] As discussed previously, in order to improve the polarizationseparation characteristics (more specifically, in order to reduceincident angle dependency and wavelength dependency), it is desirable tominimize the pitch of the periodic fine structure on the structuralbirefringent polarizing plate 200 to the smallest possible levelrelative to the wavelength of light. However, there is a manufacturallimit to make the periodic structure finer. This embodiment takes intoaccount the layout of the structural birefringent polarizing plate 200and thereby compensates for the polarization separation characteristicsof the structural birefringent polarizing plate 200.

[0128]FIG. 8 is a plan view schematically illustrating the structure ofa main part of a projector PJ3 in a third embodiment. The structure ofthe projector PJ3 is similar to that of the projector PJ1 of the firstembodiment, except that the structural birefringent polarizing plate 200is inclined to the illumination optical axis L (that is, the center axisof light illuminating the liquid crystal device).

[0129] The inclination of the structural birefringent polarizing plate200 to the illumination optical axis L virtually reduces the pitch ofthe fine periodic structure relative to the incident light along theillumination optical axis L. Such layout of the polarizing plate 200improves the polarization separation characteristics of the polarizingplate 200, thus attaining a projector that stably displayshigh-contrast, bright images.

[0130] It is desirable that the structural birefringent polarizing plate200 has a greater angle of inclination to the illumination optical axisL. The preferable setting for the angle of inclination is about 45degrees, by taking into account the loss of light in the polarizingplate 200 and the treatment of the reflected light from the polarizingplate 200. In the case of such setting for the angle of inclination, thelight reflected by the structural birefringent polarizing plate 200 isemitted in the direction of about 90 degrees relative to theillumination optical axis L. This reflected light has substantially noadverse effects on other optical elements.

[0131] Setting about 45 degrees to the angle of inclination of thestructural birefringent polarizing plate 200 to the illumination opticalaxis L is equivalent to increasing the dimension of the polarizing plate200 in the Z direction. A greater space is thus required to locate thestructural birefringent polarizing plate 200 on the light incoming sideof the liquid crystal device 300.

[0132] FIGS. 9(A) and 9(B) show modified examples of the structuralbirefringent polarizing plate of FIG. 8. FIG. 9(A) shows a structuralbirefringent polarizing plate 200C that is bent at one position alongthe Y axis to a V shape, and FIG. 9(B) shows a structural birefringentpolarizing plate 200D that is bent at three positions to a W shape. Thelayout of dividing the structural birefringent polarizing plate 200 intoa plurality of areas and arranging each area inclined to theillumination optical axis L decreases the dimension of the structuralbirefringent polarizing plate in the Z direction, thus relativelyreducing the space required for the structural birefringent polarizingplate.

[0133] The structural birefringent polarizing plate 200C shown in FIG.9(A) causes the reflected light to be emitted in the directionsubstantially perpendicular to the illumination optical axis L. Thereflected light has substantially no adverse effects on other opticalelements and is thus readily treated. Incidence of light from the lightoutgoing side often causes malfunction of the liquid crystal device.Because of the feature discussed above, the structural birefringentpolarizing plate 200C may be applied for the polarizer disposed on thelight outgoing side of the liquid crystal device. The structuralbirefringent polarizing plate 200D shown in FIG. 9(B), on the otherhand, returns part of the reflected light to the light source device 110(see FIG. 8) for recycling.

[0134] Either of the structural birefringent polarizing plates 200C and200D may be arranged in an inverted orientation. For example, to changethe light incoming surface to the light outgoing surface of thestructural birefringent polarizing plate 200C shown in FIG. 9(A), oneridge line defined by two areas of the polarizing plate 200C may befaced to the liquid crystal device 300.

[0135] In both the examples of FIGS. 9(A) and 9(B), the plurality ofareas in the structural birefringent polarizing plate are all inclinedto the illumination optical axis L. Part of the areas may alternativelybe arranged perpendicular to the illumination optical axis L. Ingeneral, at least one of the plurality of areas should be inclined tothe illumination optical axis L.

[0136] In the examples of FIGS. 9(A) and 9(B), the display area of theliquid crystal device has a rectangular shape having longer sides in theX direction and shorter sides in the Y direction. As discussed above,the examples of FIGS. 9(A) and 9(B) use the structural birefringentpolarizing plates 200C and 200D, which are respectively divided into aplurality of areas along the Y axis. It is, however, preferable to applythe structural birefringent polarizing plate divided into a plurality ofareas along the X axis for the liquid crystal device having therectangular display area. Namely it is desirable to divide thestructural birefringent polarizing plate along the longer sides of therectangular display area. The plurality of areas are then aligned alongthe shorter sides of the rectangular display area. Compared with thestructural birefringent polarizing plates 200C and 200D of FIGS. 9(A)and 9(B), this arrangement relatively reduces the thickness of thestructural birefringent polarizing plate in the Z direction.

[0137] D. Fourth Embodiment

[0138]FIG. 10 is a plan view schematically illustrating the structure ofa main part of a projector PJ4 in a fourth embodiment. Like theprojector PJ3 of the third embodiment, in this projector PJ4, thestructural birefringent polarizing plate 200 is inclined to theillumination optical axis L. More specifically, the structuralbirefringent polarizing plate 200 is inclined at an angle of 45 degreesto the illumination optical axis L.

[0139] This layout of the structural birefringent polarizing plate 200enables the projector PJ4 to utilize the Y polarized light reflected bythe structural birefringent polarizing plate 200 as the illuminationlight.

[0140] The layout of the structural birefringent polarizing plate 200shown in FIG. 10 enables an L-shaped layout of the projector PJ4. Thisrelatively decreases the dimension of the casing, which covers over theprojector, either in the X direction or in the Z direction, thusreducing the whole size of the projector. The decreased dimension in theZ direction is preferable for rear-type projectors, whereas thedecreased dimension in the X direction is preferable for vertical-typeprojectors, in which the light source device 110 is located on thebottom.

[0141] E. Fifth Embodiment

[0142] In the case where the polarizer including the light reflectivepolarizing plate is disposed on the light outgoing side of the liquidcrystal device, care must be taken in preventing a non-requiredpolarized light reflected by the light reflective polarizing plate fromentering the light outgoing surface of the liquid crystal device. Thisis because thin film transistors (TFT) often applied as active switchingelements for the liquid crystal device may malfunction in response tolight entering the light outgoing side of the liquid crystal device.

[0143] A polarization beam splitter having a polarization separationfilm has recently been applied for the polarizer including the lightreflective polarizing plate (for example, JAPANESE PATENT LAID-OPENGAZETTE No. 7-306405). The polarization beam splitter has tworectangular prisms and a polarization separation film formed on aninterface of the two rectangular prisms. The polarization beam splitteris arranged to make its polarization separation film inclined at anangle of about 45 degrees to the illumination optical axis. Arrangementof such a polarization beam splitter on the light outgoing side of theliquid crystal device causes the light reflected by the polarizationseparation film to be emitted in a direction substantially perpendicularto the illumination optical axis, thus effectively preventingmalfunction of the liquid crystal device.

[0144] However, the dimension of the polarization beam splitter alongthe illumination optical axis is set to be substantially equal to thedimension of the longer sides of the rectangular display area on theliquid crystal device. This undesirably increases the total size of thepolarizer. A relatively large space is thus required to locate thepolarizer on the light outgoing side of the liquid crystal device. Thisleads to an increase in size of the projector. The long distance betweenthe liquid crystal device and the projection optical system requires alarge-diametral projection lens, which raises the manufacturing cost ofthe projection optical system.

[0145] The embodiment discussed below locates a polarizer including alight reflective polarizing plate on the light outgoing side of theliquid crystal device, so as to improve the light resistance and heatresistance of the polarizer while reducing the total size of thepolarizer, which includes the light reflective polarizing plate and aprism.

[0146]FIG. 11 is a sectional view schematically illustrating thestructure of a first light reflective polarizer 1 in a fifth embodiment.The light reflective polarizer 1 includes a prism 10, a light reflectivepolarizing plate 20, and a light absorbing polarizing plate 30.

[0147] The prism 10 is a light transmissive body having a light incomingsurface S1i and a light outgoing surface S1o, which are not parallel toeach other. More specifically, the prism is a glass columnar body havinga quasi-triangular cross section, where an angle (vertical angle) αdefined by the light incoming surface S1i and the opposite lightoutgoing surface S1o is set to a specific value. The vertical angle awill be discussed later.

[0148] The light reflective polarizing plate 20 is an optical elementthat divides non-polarized light into two different polarized lightshaving different polarizing directions with little light absorption. Thelight reflective polarizing plate 20 of this embodiment may beconstructed by any one of the following optical elements:

[0149] (a) a polarization separation element consisting of dielectricmulti-layered films;

[0150] (b) a structural birefringent polarizing plate having aperiodical fine structure;

[0151] (c) a multi-layered polymer polarizing plate obtained bylaminating layers of an organic material having anisotropy of refractiveindex (birefringence), such as a liquid crystal material (for example,DBEF manufactured by 3M Corp.);

[0152] (d) an optical element obtained by combining a circularpolarization reflector (for example, cholesteric liquid crystal), whichdivides non-polarized light into a right-handed circularly polarizedlight and left-handed circularly polarized light, with a λ/4 retardationplate;

[0153] (e) an optical element that utilizes the Brewster angle toseparate a reflected polarized light from a transmitted polarized light(for example, see SID'92 DIGEST p427); and

[0154] (f) a hologram optical element utilizing hologram.

[0155] The light absorbing polarizing plate 30 absorbs one linearlypolarized light out of two linearly polarized lights havingperpendicular polarizing directions, while transmits the other linearlypolarized light. The light absorbing polarizing plate 30 may be obtainedby uniaxially orienting a film impregnated with iodine or a dye.

[0156] The light absorbing polarizing plate 30 is used, since thepolarization separation characteristics of the light reflectivepolarizing plate 20 often have incident angle dependency. The divergentlight or the convergent light entering the light reflective polarizingplate 20 is transmitted with the degree of polarization, which varieswith a variation in incident angle. The light absorbing polarizing plate30 disposed on the light outgoing side of the light reflectivepolarizing plate 20 enhances the degree of polarization of thetransmitted light. The light absorbing polarizing plate 30 is arrangedto make the direction of its transmission axis substantially coincidentwith the polarizing direction of the transmitted light. The lightreflective polarizer 1 having the above structure thus emits thepolarized light in a substantially one polarizing state, that is, withthe high degree of polarization.

[0157] Non-polarized light entering the light incoming surface S1i ofthe prism 10 along the illumination optical axis L is divided into twolinearly polarized lights having perpendicular polarizing directions bythe light reflective polarizing plate 20 formed on the light outgoingsurface S1o. One linearly polarized light is transmitted through thelight reflective polarizing plate 20 and further through the lightabsorbing polarizing plate 30 and is emitted. The other linearlypolarized light (X polarized light) is reflected by the light reflectivepolarizing plate 20 and re-enters the prism 10. In this embodiment, thepolarized light transmitted through the light reflective polarizingplate 20 may be referred to as the transmitted light, whereas thepolarized light reflected by the light reflective polarizing plate 20may be referred to as the reflected light.

[0158] The reflected light (the return light) re-entering the prism 10is totally reflected by the light incoming surface S1i and is emittedfrom a surface Sα opposite to the vertical angle α. Namely very littlelight is emitted from the light incoming surface S1i to the outside ofthe prism 10.

[0159]FIG. 12 shows setting for the vertical angle a of the prism 10.The light entering the light incoming surface S1i at an incident angleθ1 is reflected by the light reflective polarizing plate 20 and thenenters the light incoming surface S1i at an incident angle θ. When theincident angle θ satisfies Relation (1) given below, the reflected light(the return light) is totally reflected by the light incoming surfaceS1i. The incident angle θ is specified by the incident angle θ1, thevertical angle α of the prism, and a refractive index n of the prism.When the vertical angle a satisfies Relation (2) given below, the returnlight is totally reflected by the light incoming surface S1i. Settingthe vertical angle α in this manner effectively prevents the returnlight from being emitted from the light incoming surface S1i to theoutside of the prism 10.

θ≦sin⁻¹(1/n)   (1)

α≧(sin⁻¹(1/n·sinθ1)+sin ⁻¹(1/n))/2   (2)

[0160] For example, when the maximum incident angle θ1 of the lightentering the prism is ±11.3 degrees (this is equivalent to the case inwhich the F number of the integrator optical system of the projector isabout 2.5) and the refractive index n of the prism is equal to 1.52,setting the vertical angle α of the prism to not lower than about 24.3degrees causes the return light to be totally reflected by the lightincoming surface S1i.

[0161] A dimension BC of the surface Sα opposite to the vertical angle αin the direction of the illumination optical axis L is set to be about0.45 times a dimension AB of the light incoming surface S1i in the Ydirection. The shorter dimension BC of the prism 10 than the dimensionAB desirably reduces the total size of the light reflective polarizer 1.

[0162] It is desirable that a phase change, which affects the polarizingstate of light, hardly arises inside the prism 10. An internal stress oran external stress is often produced to cause a phase change in thevicinity of the vertexes of the prism 10, due to its shape. In order tomaintain the polarizing state of the light passing through the prism 10,the prism 10 of this embodiment is composed of a glass material having arelatively small photoelastic constant. By considering the sensitivityof the human eye, it is preferable that the photoelastic constant of theglass material is not higher than about 1 nm/cm/10⁵ Pa. The prismcomposed of such a glass material decreases the degree of the possiblyarising phase change and practically equalizes the in-plane distributionof the degree of polarization. Any plastic material having a relativelysmall photoelastic constant may replace the glass material.

[0163] The light reflective polarizer 1 shown in FIG. 11 includes thelight reflective polarizing plate 20 with very little light absorptionand accordingly has the improved light resistance and heat resistance.Even when the light entering the polarizer has a high intensity, thepolarizer exerts the stable polarization separation characteristics. Inthe prism 10, the angle (vertical angle) defined by the light incomingsurface S1i and the light outgoing surface S1o is set to cause thereflected light (the return light) from the light reflective polarizingplate 20 to be totally reflected by the light incoming surface S1i ofthe prism 10. This setting effectively prevents the non-requiredpolarized light (the reflected light) from being emitted from the lightincoming surface S1i to the outside. The arrangement of locating thelight reflective polarizer on the light outgoing side of the liquidcrystal device in the projector does not cause the light to enter thelight outgoing surface of the liquid crystal device, thus effectivelypreventing malfunction of the liquid crystal device.

[0164] In this embodiment, the prism 10, the base member of the lightreflective polarizing plate 20, and the base member of the lightabsorbing polarizing plate 30 have substantially identical refractiveindexes. The optical integration of the prism 10, the light reflectivepolarizing plate 20, and the light absorbing polarizing plate 30decreases the loss of light at each interface and facilitates handlingof the light reflective polarizer 1. The optical integration alsoenhances the utilization efficiency of light in the polarizer 1 andreduces the return light into the prism 10. It should be noted that thelight absorbing polarizing plate 30 may be omitted in the case where thepolarized light (the transmitted light) emitted from the lightreflective polarizing plate 20 has a high degree of polarization.

[0165] In the polarizer 1 shown in FIG. 11, antireflection coatings areformed on the light incoming surface S1i and the surface Sα. Suchcoatings enable the external light to mostly enter the light incomingsurface S1i of the prism 1, while causing the light totally reflected bythe light incoming surface S1i to be mostly emitted from the surface Sαof the prism 1. The antireflection coatings of different structures areformed on the light incoming surface S1i and the surface Sα according tothe incident angle of light.

[0166] In the actual state, however, the light entering the surface Sαof the prism 10 may be reflected by the surface Sα and re-enters thelight reflective polarizing plate 20. FIG. 13 shows a modified exampleof the polarizer 1 of FIG. 11. A polarizer 1′ shown in FIG. 13 has thestructure similar to that of the polarizer 1 shown in FIG. 11, exceptthe shape of a prism 10′. More specifically, the primary difference is asurface (opposite surface) Sα′ opposite to the vertical angle α definedby the light incoming surface S1i and the light outgoing surface S1o ofthe prism 10′. The surface Sα′ is set to cause the linearly polarizedlight (the X polarized light) totally reflected by the light incomingsurface S1i of the prism 10′ to enter the surface Sα′ at virtually rightangles. An angle β defined by the light incoming surface S1i and thesurface Sα′ is set substantially equal to the incident angle θ of thelight, which has been reflected from the light reflective polarizingplate 20 and is to be totally reflected by the light incoming surfaceS1i.

[0167] Application of this polarizer 1′ causes the light entering thesurface Sα′ to be mostly emitted from the surface Sα′, thussignificantly reducing the light re-entering the light reflectivepolarizing plate 20. In the polarizer 1′, the incident angle (almost 0degree) of the light entering the light incoming surface S1i is equal tothe incident angle of the light entering the surface Sα′. Theantireflection coatings formed on the two faces S1i and Sα′ mayaccordingly have a common structure.

[0168]FIG. 14 is a sectional view schematically illustrating thestructure of a second light reflective polarizer 2 in the fifthembodiment. The light reflective polarizer 2 has a similar structure tothat of the light reflective polarizer 1 shown in FIG. 11, except that asecond prism 40 is disposed on the light outgoing side of the lightabsorbing polarizing plate 30.

[0169] The light reflective polarizer 2 shown in FIG. 14 exerts theadditional advantages discussed below, in addition to the sameadvantages as those of the light reflective polarizer 1 shown in FIG.11.

[0170] In the example of FIG. 14, an identical prism is applied for thetwo prisms 10 and 40. The two prisms 10 and 40 are located inversely inthe Y direction. The two prisms 10 and 40 have the same refractiveindex. The light outgoing surface S1o of the first prism 10 issubstantially parallel to a light incoming surface S2i of the secondprism 40. The light incoming surface S1i of the first prism 10 issubstantially parallel to a light outgoing surface S2o of the secondprism 40. Accordingly there is substantially no change in travellingdirection of the light passing through the light reflective polarizer 2.Namely the travelling direction of the light entering the lightreflective polarizer 2 is virtually coincident with the travellingdirection of the light emitted from the light reflective polarizer 2.This arrangement advantageously facilitates the assembly of an opticalsystem including the light reflective polarizer 2 in combination withanother optical part.

[0171] The two prisms 10 and 40 may be composed of different materials.For example, materials having optimal physical properties (for example,refractive index and photoelastic constant) may be selected respectivelyfor the prisms 10 and 40, according to the application of the lightreflective polarizer 2. Even in the case where the two prisms 10 and 40have different refractive indexes, adjustment of the vertical angle ofthe second prism makes the travelling direction of the light enteringthe light reflective polarizer substantially coincident with thetravelling direction of the light emitted from the light reflectivepolarizer.

[0172] It should be noted that the materials having high refractiveindex and small photoelastic constant are expensive. In the arrangementof disposing the light reflective polarizers 2 on the light incomingside or on the light outgoing side of the liquid crystal device in theprojector, the material having a high refractive index and a smallphotoelastic constant (for example, the material having a photoelasticconstant of not higher than about 1 nm/cm/10⁵ Pa) is applied for theprism closer to the liquid crystal device, while some inexpensivematerial may be applied for the other prism. This arrangement desirablyreduces the manufacturing cost with little deterioration of the opticalcharacteristics of the light reflective polarizer 2.

[0173] The second prism 40 is not required to cause total reflection.The travelling direction of the light emitted from the light reflectivepolarizer 2 is thus regulated by adequately setting the refractive indexand the vertical angle of the second prism 40. This enhances the degreeof freedom in layout of the other optical parts and facilitates theconstruction of, for example, an elevation angle projection opticalsystem.

[0174] In this embodiment, the first prism 10, the base member of thelight reflective polarizing plate 20, the base member of the lightabsorbing polarizing plate 30, and the second prism 40 havesubstantially identical refractive indexes. The optical integration ofthe first prism 10, the light reflective polarizing plate 20, the lightabsorbing polarizing plate 30, and the second prism 40 decreases theloss of light at each interface and facilitates handling of the lightreflective polarizer 2. The optical integration also enhances theutilization efficiency of light in the polarizer 2 and reduces thereturn light into the prism 10. It should be noted that the lightabsorbing polarizing plate 30 may be omitted as in the case of the lightreflective polarizer 1.

[0175]FIG. 15 is a sectional view schematically illustrating thestructure of a third light reflective polarizer 3 in the fifthembodiment. In the light reflective polarizer 2 of FIG. 14, the lightabsorbing polarizing plate 30 is located on the light incoming surfaceS2i of the second prism 40. On the other hand, in the light reflectivepolarizer 3, the light absorbing polarizing plate 30 is located on thelight outgoing surface S2o of the second prism 40. The light reflectivepolarizer 3 exerts the additional advantages discussed below, inaddition to the same advantages as those of the light reflectivepolarizer 2 shown in FIG. 14.

[0176] The light absorbing polarizing plate 30 absorbs light and therebygenerates heat. In the light reflective polarizer 2 shown in FIG. 14,the heat generated by the light absorbing polarizing plate 30 affectsthe second prism 40 and the light absorbing polarizing plate 30 itselfto cause a phase change or deterioration of the polarizationcharacteristics. On the other hand, in the light reflective polarizer 3shown in FIG. 15, the heat generated by the light absorbing polarizingplate 30 is quickly released to the outside space. This arrangement thusdesirably relieves the adverse effects of the heat generated by thelight absorbing polarizing plate 30 on the peripheral optical elements,such as the second prism 40.

[0177] The arrangement of locating the light absorbing polarizing plate30 on the light outgoing surface S2o of the second prism 40 enables thesmaller incident angle of the transmitted light entering the lightabsorbing polarizing plate 30, thus advantageously improving thepolarization characteristics of the light absorbing polarizing plate 30.

[0178]FIG. 16 is a sectional view schematically illustrating thestructure of a fourth light reflective polarizer 4 in the fifthembodiment. The light reflective polarizer 4 has a similar structure tothat of the light reflective polarizer 3 shown in FIG. 15, except that astructural birefringent polarizing plate 21 is applied for the lightreflective polarizing plate 20. The structural birefringent polarizingplate 21 may be any of the structural birefringent polarizing platesdiscussed previously with FIGS. 2(A) and FIG. 2(B). The example of FIG.16 uses the structural birefringent polarizing plate shown in FIG. 2(A).

[0179] The structural birefringent polarizing plate 21 has a lighttransmissive substrate 210, which is in close contact with the lightincoming surface of the second prism 40, and a periodical fine structure(metal thin film) 211, which faces the first prism 10 across a smallspace. Light enters the fine periodic structure 211 across the smallspace and goes to the light transmissive substrate 210. Providing such asmall space enhances the polarization separation characteristics of thestructural birefringent polarizing plate 21.

[0180] The fine periodic structure 211 is periodically arranged in aspecific direction that is perpendicular to the intersection line of thelight incoming surface S1i and the light outgoing surface S1o of thefirst prism 10 (that is, the X direction) and is parallel to the lightoutgoing surface S1o. The grooves 212 extend in the X direction. Thestructural birefringent polarizing plate 21 is thus inclined to theillumination optical axis L. Such arrangement practically decreases thepitch of the fine periodic structure relative to the illumination lightand thereby improves the optical characteristics of the structuralbirefringent polarizing plate.

[0181] In the oblique layout of the structural birefringent polarizingplate 21 to the illumination optical axis L, it is preferable that thedirection of the periodical arrangement of the fine periodic structure211 is inclined to the illumination optical axis L. The layout of thestructural birefringent polarizing plate to make the periodicalarrangement of the fine periodic structure perpendicular to theillumination optical axis L does not practically decrease the pitch ofthe fine periodic structure relative to the illumination light, thushaving difficulties in improving the optical characteristics.

[0182] In the example of FIG. 16, the refractive index of the lighttransmissive substrate 210 is set practically equal to the refractiveindex of the second prism 40. This reduces the loss of light occurringat the interface between the structural birefringent polarizing plate 21and the second prism 40.

[0183] The light reflective polarizer 4 shown in FIG. 16 exerts thesimilar advantages to those of the light reflective polarizer 3 shown inFIG. 15. In the example of FIG. 16, the structural birefringentpolarizing plate 21 having relatively small incident angle dependency ofthe polarization separation characteristics is applied for the lightreflective polarizing plate and accordingly ensures the excellentpolarization separation characteristics even when light having a highintensity or light having a large incident angle enters the lightreflective polarizer 4.

[0184] The structural birefringent polarizing plate 21 applied for thelight reflective polarizing plate 20 shown in FIG. 15 may be replacedwith a multi-layered polarizing plate, which is composed of thin filmswith anisotropy of refractive index. The multi-layered polarizing plateis obtained by alternately laminating the first films with birefringenceand the second films without birefringence as discussed previously withFIG. 6.

[0185] Application of the multi-layered polarizing plate for the lightreflective polarizing plate 20 exerts the similar advantages to those ofthe light reflective polarizer 3 shown in FIG. 15. The multi-layeredpolarizing plate has relatively small wavelength dependency of thepolarization separation characteristics and thus ensures excellentpolarization separation characteristics even when the incident light hasa wide wavelength domain like the visible light.

[0186] The first prism 10 in any of the polarizers 2, 3, and 4 shown inFIGS. 14, 15, and 16 may be replaced by the prism 10′ shown in FIG. 13.

[0187]FIG. 17 is a sectional view schematically illustrating thestructure of a fifth light reflective polarizer 5 in the fifthembodiment. This light reflective polarizer 5 has two polarizer elements5 a and 5 b, where the second prism 40 is disposed on the light outgoingside of the polarizer 1′ shown in FIG. 13. The two polarizer elements 5a and 5 b are connected to each other, such that the light incomingsurfaces S1i of the respective first prisms 10′ are located in asubstantially identical plane. The two polarizer elements 5 a and 5 bare arranged to be symmetrical across the illumination optical axis L.The light reflective polarizing plates 20 of the respective polarizerelements 5 a and 5 b form a V shape.

[0188] The light reflective polarizer 5 of the above construction hasthe decreased dimension in the Z direction as discussed in FIG. 9(A).This reduces the size of the light reflective polarizer, whileadvantageously making the smaller space sufficient for the lightreflective polarizer 5. Application of this light reflective polarizer 5for the projector desirably reduces the total size of the projector.

[0189] In the example of FIG. 17, the separate prisms are applied forthe second prisms 40 disposed on the light outgoing side of the twopolarizer elements 5 a and 5 b. One integral prism may alternatively beused for the second prisms 40.

[0190] In the light reflective polarizer 5 shown in FIG. 17, thepolarizer 1′ of FIG. 13 is used for the polarizer elements. Any of theother polarizers 1 to 4 may alternatively be applied for the polarizerelements. The light reflective polarizer 5 of FIG. 17 is obtained bycombining the two polarizer elements 1′. In another example, combinationof four polarizer elements selected among the polarizers 1 to 4 givesthe light reflective polarizing plates 20 forming a W shape as shown inFIG. 9(B). This further reduces the size of the light reflectivepolarizer. Application of this light reflective polarizer furtherreduces the total size of the projector. In general, a plurality ofpolarizer elements are connected in such a manner that light incomingsurfaces of respective first prisms are located in a substantiallyidentical plane.

[0191]FIG. 18 is a plan view schematically illustrating the structure ofa main part of a projector PJ5 in the fifth embodiment. The plan view ofFIG. 18 is seen from the X direction.

[0192] The projector PJ5 has a similar structure to that of theprojector PJ2 of the second embodiment (see FIG. 7(B)), except apolarizer disposed on the light outgoing side of the liquid crystaldevice 300. More specifically, the projector PJ5 uses a light reflectivepolarizer 3′, in which the first prism 10 of the light reflectivepolarizer 3 shown in FIG. 15 is replaced by the first prism 10′ shown inFIG. 13. In the projector PJ5, a superimposing lens 180′ in apolarization conversion optical system 150′ is oriented to make itsconvex surface function as the light incoming surface.

[0193]FIG. 19 shows layout of the light reflective polarizer 3′ disposedon the light outgoing side of the liquid crystal device 300 of FIG. 18.The liquid crystal device 300 typically has a rectangular display area.The light reflective polarizer 3′ is arranged to make an intersectionline 11 defined by its light incoming surface S1i and light outgoingsurface S1o substantially parallel to longer sides 301 of the displayarea of the liquid crystal device 300 (that is, the X direction).

[0194] Compared with the arrangement of making the intersection line 11of the light incoming surface S1i and the light outgoing surface S1osubstantially parallel to shorter sides of the display area of theliquid crystal device 300 (that is, the Y direction), this arrangementof the light reflective polarizer 3′ shown in FIG. 19 relativelydecreases the dimension of the light reflective polarizer 3′ along theillumination optical axis L (that is, in the Z direction). As discussedpreviously with FIG. 12, the size of the light reflective polarizer 3′in the Z direction is determined as tanα times the dimension AB of thelight incoming surface S1i of the first prism 10. The layout shown inFIGS. 18 and 19 shortens the distance between the liquid crystal device300 and the projection optical system 500, thus desirably reducing thesize of the projection lens and the whole projector while cutting themanufacturing cost.

[0195] As described above, application of the light reflective polarizer3′ having the improved light resistance and the heat resistance enablesthe projector PJ5 to generate polarized light having a high degree ofpolarization and displays high-contrast images. The light reflectivepolarizer 3′ also prevents a non-required polarized light from returningto the liquid crystal device 300. This effectively prevents malfunctionof the liquid crystal device 300 and ensures stable display ofhigh-quality images, even when the light entering the polarizer has ahigh intensity.

[0196] In the projector PJ5, the light reflective polarizer 3′ islocated only on the light outgoing side of the liquid crystal device300. The light reflective polarizer 3′ may be disposed only on the lightincoming side of the liquid crystal device 300 according to the presenceor absence of the polarization conversion optical system 150′, that is,according to the thermal load applied to the polarizer. Morespecifically, the light reflective polarizer 3′ may be disposed at leaston the light incoming side of the liquid crystal device 300 in theabsence of the polarization conversion optical system 150′ (in thiscase, the integrator optical system shown in FIG. 1 is adopted). In thepresence of the polarization conversion optical system 150′, on theother hand, the light reflective polarizer 3′ may be disposed at leaston the light outgoing side of the liquid crystal device 300. The lightabsorbing polarizing plate 400 may be used alone on the side without thelight reflective polarizer 3′. Such arrangement attains the sizereduction and the high performance of the projector, simultaneously withthe reduction of the manufacturing cost.

[0197] The light reflective polarizer 3′ used in the projector PJ5 maybe replaced by any of the other light reflective polarizers 1, 1′, 2, 3,4, and 5.

[0198] The present invention is not restricted to the above embodimentsor their modifications, but there may be many other modifications,changes, and alterations without departing from the scope or spirit ofthe main characteristics of the present invention. Some examples ofpossible modification are given below.

[0199] (1) In FIGS. 2(A), 2(B) and 16, the structural birefringentpolarizing plate 200 or 21 is arranged to cause light to enter thesurface with the fine periodic structure 211. The structuralbirefringent polarizing plate may alternatively be arranged to causelight to enter the surface opposite to the surface with the fineperiodic structure 211, that is, the light transmissive substrate 210.The arrangement of FIGS. 2(A), 2(B) and 16, however, relatively enhancesthe polarization separation characteristics of the structuralbirefringent polarizing plate.

[0200] (2) The above embodiments regard the single-type projector usingonly one liquid crystal device. The principle of the present inventionis also applicable to the projector using a plurality of liquid crystaldevices. The transmissive-type liquid crystal device is used in theabove embodiments. The present invention is also applicable to theprojector using a reflective-type liquid crystal device. The techniqueof the present invention is further applicable to a rear projection-typeprojector that projects and displays images on a transmissive-typescreen, as well as to the front projection-type projector.

Industrial Applicability

[0201] The present invention is applicable to diverse optical devicesutilizing polarizers, for example, projectors.

What is claimed is:
 1. A projector, comprising: a light source device;an electro-optic device that modulates light emitted from the lightsource device; two polarizers that are disposed respectively on a lightincoming side and a light outgoing side of the electro-optic device; anda projection optical system that projects light output from theelectro-optic device, wherein at least one of the two polarizers is astructural birefringent polarizing plate.
 2. The projector in accordancewith claim 1, wherein the structural birefringent polarizing plate is awiregrid polarizing plate.
 3. The projector in accordance with claim 1,wherein the structural birefringent polarizing plate comprises: a lighttransmissive crystal substrate; and a fine periodic structureperiodically formed in a predetermined direction on the lighttransmissive crystal substrate.
 4. The projector in accordance with anyone of claims 1 to 3, wherein the structural birefringent polarizingplate is inclined to a center axis of light illuminating theelectro-optic device.
 5. The projector in accordance with claim 4,wherein the structural birefringent polarizing plate is arranged at aninclination of about 45 degrees relative to the center axis.
 6. Theprojector in accordance with any one of claims 1 to 3, wherein thestructural birefringent polarizing plate is divided into a plurality ofareas, and at least one of the plurality of areas is inclined to acenter axis of light illuminating the electro-optic device.
 7. Theprojector in accordance with claim 6, wherein at least one of theplurality of areas in the structural birefringent polarizing plate isarranged at an inclination of about 45 degrees relative to the centeraxis.
 8. The projector in accordance with any one of claims 1 to 3,wherein a light absorbing polarizing plate is further arranged on alight outgoing side of the structural birefringent polarizing plate. 9.The projector in accordance with claim 8, wherein a light transmissivecrystal substrate is further arranged on a light outgoing side of thelight absorbing polarizing plate, and the light transmissive crystalsubstrate is appressed to the light absorbing polarizing plate.
 10. Theprojector in accordance with any one of claims 1 to 3, wherein a lightreflective polarizing plate is further arranged on a light outgoing sideof the structural birefringent polarizing plate.
 11. The projector inaccordance with claim 10, wherein the light reflective polarizing plateis a multi-layered polarizing plate that is obtained by alternativelylaminating a birefringent film and non-birefringent film.
 12. Aprojector, comprising: a light source device; an electro-optic devicethat modulates light emitted from the light source device; twopolarizers that are disposed respectively on a light incoming side and alight outgoing side of the electro-optic device; and a projectionoptical system that projects light output from the electro-optic device,at least one of the two polarizers comprising: a first prism having alight incoming surface and a light outgoing surface, which face to eachother in a non-parallel orientation; and a light reflective polarizingplate that is disposed on a side of the light outgoing surface of thefirst prism, wherein the light reflective polarizing plate divides lightemitted from the first prism into first and second polarized lightshaving different polarizing directions, and transmits the firstpolarized light while reflecting the second polarized light, and anangle defined by the light incoming surface and the light outgoingsurface of the first prism is set to cause the second polarized light,which has been reflected by the light reflective polarizing plate andreturned to the first prism, to be totally reflected by the lightincoming surface.
 13. The projector in accordance with claim 12, whereinthe first prism has an intersection line defined by the light incomingsurface and the light outgoing surface, the intersection line beingsubstantially parallel to longer sides of a rectangular display area onthe electro-optic device.
 14. The projector in accordance with claim 12,wherein a face of the first prism opposite to a vertical angle definedby the light incoming surface and the light outgoing surface of thefirst prism is set to cause the second polarized light totally reflectedby the light incoming surface to enter the opposite face atsubstantially right angles.
 15. The projector in accordance with claim12, wherein the first prism is composed of a material having aphotoelastic constant of not higher than about 1 nm/cm/10⁵ Pa.
 16. Theprojector in accordance with claim 12, further comprising a secondprism, which is disposed on a light outgoing side of the lightreflective polarizing plate to receive the first polarized lighttransmitted through the light reflective polarizing plate.
 17. Theprojector in accordance with claim 16, wherein at least one of the firstprism and the second prism is composed of a material having aphotoelastic constant of not higher than about 1 nm/cm/10⁵ Pa.
 18. Theprojector in accordance with claim 16, wherein the second prism isarranged to make a travelling direction of the first polarized lightemitted via the second prism substantially coincide with a travellingdirection of light entering the first prism.
 19. The projector inaccordance with any one of claims 12 to 18, wherein a light absorbingpolarizing plate is disposed on a light outgoing side of the lightreflective polarizing plate.
 20. The projector in accordance with anyone of claims 12 to 18, wherein the light reflective polarizing plate isa structural birefringent polarizing plate.
 21. The projector inaccordance with claim 20, wherein the structural birefringent polarizingplate comprises a fine periodic structure periodically formed along apredetermined direction, and the predetermined direction issubstantially perpendicular to an intersection line defined by the lightincoming surface and the light outgoing surface of the first prism. 22.The projector in accordance with any one of claims 12 to 18, wherein thelight reflective polarizing plate is a multi-layered polarizing platethat is obtained by alternatively laminating a birefringent film andnon-birefringent film.
 23. A projector, comprising: a light sourcedevice; an electro-optic device that modulates light emitted from thelight source device; two polarizers that are disposed respectively on alight incoming side and a light outgoing side of the electro-opticdevice; and a projection optical system that projects light output fromthe electro-optic device, at least one of the two polarizers including aplurality of polarizer elements, each polarizer element comprising: afirst prism having a light incoming surface and a light outgoingsurface, which face to each other in a non-parallel orientation; and alight reflective polarizing plate that is disposed on a side of thelight outgoing surface of the first prism, wherein the plurality ofpolarizer elements are jointed in such a manner that the respectivelight incoming surfaces of the first prisms are located in a virtuallysame plane, wherein in the each polarizer element, the light reflectivepolarizing plate divides light emitted from the first prism into firstand second polarized lights having different polarizing directions, andtransmitting the first polarized light while reflecting the secondpolarized light, and an angle defined by the light incoming surface andthe light outgoing surface of the first prism is set to cause the secondpolarized light, which has been reflected by the light reflectivepolarizing plate and returned to the first prism, to be totallyreflected by the light incoming surface.
 24. A polarizer, comprising: afirst prism having a light incoming surface and a light outgoingsurface, which face to each other in a non-parallel orientation; and alight reflective polarizing plate that is disposed on a side of thelight outgoing surface of the first prism, wherein the light reflectivepolarizing plate divides light emitted from the first prism into firstand second polarized lights having different polarizing directions, andtransmits the first polarized light while reflecting the secondpolarized light, and an angle defined by the light incoming surface andthe light outgoing surface of the first prism is set to cause the secondpolarized light, which has been reflected by the light reflectivepolarizing plate and returned to the first prism, to be totallyreflected by the light incoming surface.
 25. The polarizer in accordancewith claim 24, a face of the first prism opposite to a vertical angledefined by the light incoming surface and the light outgoing surface ofthe first prism is set to cause the second polarized light totallyreflected by the light incoming surface to enter the opposite face atsubstantially right angles.
 26. The polarizer in accordance with claim24, wherein the first prism is composed of a material having aphotoelastic constant of not higher than about 1 nm/cm/10⁵ Pa.
 27. Thepolarizer in accordance with claim 24, further comprising a secondprism, which is disposed on a light outgoing side of the lightreflective polarizing plate to receive the first polarized lighttransmitted through the light reflective polarizing plate.
 28. Thepolarizer in accordance with claim 27, wherein at least one of the firstprism and the second prism is composed of a material having aphotoelastic constant of not higher than about 1 nm/cm/10⁵ Pa.
 29. Thepolarizer in accordance with claim 27, wherein the second prism isarranged to make a travelling direction of the first polarized lightemitted via the second prism substantially coincide with a travellingdirection of light entering the first prism.
 30. The polarizer inaccordance with any one of claims 24 to 29, wherein a light absorbingpolarizing plate is disposed on a light outgoing side of the lightreflective polarizing plate.
 31. The polarizer in accordance with anyone of claims 24 to 29, wherein the light reflective polarizing plate isa structural birefringent polarizing plate.
 32. The polarizer inaccordance with claim 31, wherein the structural birefringent polarizingplate comprises a fine periodic structure periodically formed along apredetermined direction, and the predetermined direction issubstantially perpendicular to an intersection defined by the lightincoming surface and the light outgoing surface of the first prism. 33.The polarizer in accordance with any one of claims 24 to 29, wherein thelight reflective polarizing plate is a multi-layered polarizing platethat is obtained by alternatively laminating a birefringent film andnon-birefringent film.
 34. A polarizer comprising a plurality ofpolarizer elements, each polarizer element comprising: a first prismhaving a light incoming surface and a light outgoing surface, which faceto each other in a non-parallel orientation; and a light reflectivepolarizing plate that is disposed on a side of the light outgoingsurface of the first prism, wherein the plurality of polarizer elementsare jointed in such a manner that the respective light incoming surfacesof the first prisms are located in a virtually same plane, wherein inthe each polarizer element, the light reflective polarizing platedivides light emitted from the first prism into first and secondpolarized lights having different polarizing directions, andtransmitting the first polarized light while reflecting the secondpolarized light, and an angle defined by the light incoming surface andthe light outgoing surface of the first prism is set to cause the secondpolarized light, which has been reflected by the light reflectivepolarizing plate and returned to the first prism, to be totallyreflected by the light incoming surface.